Computer, communication, and other electronic systems are often expandable or networked through cables. The cables may be plugged into sockets or other connectors. Cables could carry electronic signals using a variety of protocols, such as Universal-Serial-Bus (USB), small-computer system interface (SCSI), Ethernet, Token Ring, Serial AT-Attachment (SATA), Peripheral Component Interconnect (PCI), PCI Express (PCIe), various differential signaling schemes, and other variations, whether standardized or proprietary.
Cables can sometimes become disconnected, such as when a connector is pulled out by mistake. The wires inside the cable may also become frayed and break, or the connector may fail. The far-end receiver is then no longer able to receive the signal sent from the near-end transmitter.
Unplug detectors are often included in signaling chips and other devices. These unplug detectors examine the signal levels on the cable lines and report when a failure is detected. However, such detectors may have significant delays in reporting cable breaks. These reporting delays are undesirable.
FIG. 1 shows a prior art unplug detector. A circuit on the transmitting side generates a signal SIG that is input to transmitter 10. Transmitter 10 drives one or more lines of cable 20 high and low to carry the signal to receiver 12. Receiver 12 detects the signal and amplifies or otherwise recovers the signal for use by far-end circuitry.
There may be periods of time when signaling stops or pauses. During these pauses when signal SIG is not active, a detect signal DET is driven out onto cable 20 by detect driver 14. Detect sensor 15 senses the voltage changes on cable 20 when detect driver 14 is driving the detect signal and generates an UNPLUG signal when the sensed voltages indicate that a break has occurred in cable 20.
FIG. 2 shows that cable unplug detection occurs when signaling is paused. Signal SIG is pulsed and varied to carry information from the transmitter to the receiver. During the time SIG is active, unplug detection does not occur. After a period of time, signal SIG stops pulsing and is idle. Perhaps no more information needs to be transmitted, or a timeout occurs, or the end of a frame is reached. During this pause in signaling, detect signal DET is activated, and detect driver 14 drives a detect signal onto cable 20. Detect sensor 15 then senses the voltage or voltage changes on cable 20 and activates unplug signal UNPLUG when conditions are met that indicate a cable break.
However, the cable break may have occurred much earlier, such as at time A. The unplug signal is not activated until time B, when detection occurs during the pause in signaling. Thus the communication system is not notified of the cable break until time B, even though the cable break occurred at time A.
The delay in detection may be significant. For example, the average delay or latency for detection may be 20 ms after the signal is paused. This long delay is undesirable, because the unplug detector can't detect the unplug event instantly. Hence, the system may fail to work because the unplug information is not obtained accurately.
What is desired is a cable unplug detector that does not have a long latency. A cable unplug detector that does not have to wait for signaling to pause is desirable to reduce latency. An unplug detection circuit is desired that performs detection while signaling is occurring is desirable. An in-situ unplug detector is desired.